The present invention relates to Asynchronous Transfer Mode (ATM) networks, and more particularly to a method and system for providing an Available Bit Rate (ABR) interface to a non ATM bandwidth adjustable Virtual Path Connection (CBR VPC).
High Speed Communication Networks
In modern telecommunication networks, different types of applications must share the same transmission media, and networks equipment must be able to support these different services while guaranteeing to each of them a specified quality of service. While some years ago, voice and data used separate networks, they now share bandwidth of the same links. For the last three years, standards organizations have worked to define transmission modes, such as ATM (Asynchronous Transmission Mode), Frame Relay, and so forth, and inside a particular transmission mode, to specify in detail the services provided to network applications. For ATM, for instance, four different service categories exist, and a user will choose one of them based on the type of service required:
Continuous Bit Rate (CBR)
This service is intended for uncompressed voice, and highest priority applications (video). The cost of this service is the highest because the bandwidth which is reserved corresponds to the maximum rate (Peak Cell Rate PCR) at which this type of application can emit. This is the bandwidth to allocate when the quality of service, in terms of maximum Cell Transfer Delay (maxCTD) and Peak to peak Cell Delay Variation (peak to peak CDV), must be guaranteed whatever the network load conditions.
Variable Bit Rate (VBR)
This service is a compromise between the Continuous Bit Rate (CBR), which requires a lot of resources, and a service where no reservation of bandwidth would be done. Effectively here, a bandwidth comprised between the Sustainable Cell Rate (SCR) of the connection and the Peak Cell Rate (PCR) of the connection is allocated, depending on the burstiness of the traffic. When the bursts created by the application in the network are limited, a bandwidth close to the Sustainable Cell Rate (SCR) is reserved. When the bursts induced by the application are large (or may be large), a bandwidth closer to the Peak Cell Rate is reserved to avoid overloading links and buffers, and loss of data.
While the service offered here also guarantees a very low loss of packets or cells (Cell Loss Ratio CLR), the transfer delays and cell delay variations are more important than for CBR. In general, VBR can be divided into VBR Real Time (good candidate for video and data RT applications) and VBR Non Real Time (good candidate for data sensitive traffic).
Unspecified Bit Rate (UBR)
This service is totally uncontrolled. Traffic is sent in the network, and is transmitted provided that the network is not congested. When the network is congested, cells are discarded. Unlike CBR and VBR, no quality of service can be guaranteed.
Available Bit Rate (ABR)
This service provides again less quality than Variable Bit Rate (VBR), and can be used for different applications. While a minimum reservation can be done in the network to guarantee to an application a xe2x80x9cworst casexe2x80x9d behavior, the steady state behavior of the service offered corresponds to a xe2x80x9cnon reservedxe2x80x9d type of service, where nearly no resource is allocated in the network. When congestion occurs, feedback is conveyed through the network back to the traffic sources to prevent them from sending more data. This reactive system behavior is directly linked to the network size. The delay to convey back congestion information to the sources increases as a function of the network size, and may nevertheless induce losses. In this case, end users make decisions to send the data again. Here neither the delays nor the losses can be guaranteed; the service is only assumed to minimize the losses.
All these different services are proposed and used simultaneously in most networks.
Bandwidth Optimization
Most wide-area ATM networks (large country, world-wide networks) are configured so that an ATM backbone network can support communications between different ATM access networks. Such network topology allows good performance and the optimization of the network administration. Generally, the backbone network is a public ATM network, and access networks are private ATM networks. However, the backbone can be used within a single private network using, for example, lines leased from a carrier. To optimize the resources where they are most demanded, in particular the bandwidth within the backbone network, several solutions can be implemented, all taking into account the dynamic availability of the bandwidth:
1. End to End Available Bit Rate Virtual Channel Connections (ABR VCCs) for Data Traffic
This solution, as illustrated in FIG. 5, supposes the support of ABR VCCs by all end-systems (source node 1 and destination node 8). The advantage is that intermediate nodes within access networks and within the backbone network (nodes 2 to 7) have only to set an Explicit Forward Congestion Indication (EFCI) bit in the ATM cells to be compliant with the ATM Forum recommendation (ATM Forumxe2x80x94Technical Committeexe2x80x94xe2x80x9cTraffic Management Specification,xe2x80x9d version 4.0, April 96, paragraph 5.10.6, rule 1.a)). End-systems (nodes 1 and 8) connected to users (user 1 and user 2) do the most complex process, in particular:
the ABR source behavior (node 1) including:
generation of Resource Management cells (RM-cells),
insertion of RM-cells in the traffic,
computation of a transmission rate per VCC based on congestion information received from RM-cells,
dynamic traffic shaping, and
the ABR destination (node 8) behavior including:
transmission of RM-cells back to the source in response to forward RM-cells,
setting of the congestion fields within RM-cells, and
insertion of RM-cells in the traffic.
A more sophisticated implementation of the Available Bit Rate (ABR) category of service in intermediate nodes is described in the ATM Forum paragraph 5.10.6, rule 1.c). The so called xe2x80x9cswitch behaviorxe2x80x9d allows the control of congestion at queuing points, and in particular the modification of the Explicit Rate (ER) field within RM-cells for a better response to congestion and thus a lower cell loss.
2. Available Bit Rate Virtual Path Connections (ABR VPCs) in the Backbone
FIG. 6 is a view of a network comprising a first access network (access network 1) comprising an end node (node 1) connected to a user (user 1) and a source node (source node 2), a backbone network comprising a plurality of nodes (node 3, node 4, and node 9) and a second access network (access network 2) comprising a destination node (destination node 5), transit nodes (nodes 6 and 7), and an end node (node 8) connected to a user 2. An ABR VCC is established between nodes 2-5, to transmit, to node 5, traffic of end user 1 (VCC1) together with traffic of other end users (VCC3). In node 5, traffic is discriminated according to its destination, and transmitted to end user 2 (VCC2) and to other end users (VCC4).
ABR Virtual Path Connections (VPCs), as illustrated in FIG. 6, are set up in the backbone network for interconnecting access networks (access networks 1 and 2). The nodes within the access networks directly connected to the backbone network (nodes 2 and 5) use these ABR VPCs to transport VCCs (VCC1, VCC3). In order to comply with the ATM Forum recommendations (paragraph 5.10.9), these nodes implement the ABR source and destination behavior as described in paragraphs 5.10.4 to 5.10.9. Access nodes (nodes 2 and 5) must also be able to provide a fair share of the bandwidth of these Virtual Path Connections (VPCs) among the different Virtual Channel Connections (VCC1, VCC3) they support.
3. Continuous Bit Rate Virtual Path Connections (CBR VPCs) with Adjustable Bandwidth in the Backbone
FIG. 7 is a view of a network comprising a first access network (access network 1) comprising an end node (node 1) connected to a user 1 and a source node (source node 2), a backbone network comprising a plurality of nodes (nodes 3, 4, and 9) and a second access network (access network 2) comprising a destination node (destination node 5), transit nodes (nodes 6 and 7), and an end node (node 8) connected to a user 2. A CBR VCC is established between nodes 2-5, to transmit, to node 5, traffic of end user 1 (VCC1) together with traffic of other end users (VCC3). In node 5, traffic is discriminated according to its destination, and transmitted to end user 2 (VCC2) and to other end users (VCC4).
A bandwidth adjustable CBR Virtual Path Connection (VPC), as illustrated in FIG. 7, is set up in the backbone network for interconnecting the access networks (access networks 1 and 2). The nodes within the access networks directly connected to the backbone network (nodes 2 and 5) use this CBR VPC to transport VCCs. Access nodes must provide a fair share of the bandwidth of this CBR Virtual Path Connection (VPC) among the different Virtual Channel Connections (VCC1, VCC3) it supports.
This last solution implies a dynamic adjustment of the CBR VPC bandwidth according to the network availability. Each time the bandwidth of a CBR connection is modified, the Connection Admission Control (CAC) process is triggered. However, because this process requires a large amount of resources, it cannot be processed continuously. A certain degree of integration is necessary to manage the fluctuations of the network load. The response time required to adjust the bandwidth of a CBR VPC is not in the order of a millisecond, as for an ABR VPC, but in the order of a minute or more depending upon the number of voice connections established and disconnected within a given time period.
Bandwidth Adjustable Virtual Path Connections
The establishment of dynamic bandwidth adjustable Virtual Paths Connections (ABR or CBR VPCs) as shown in solutions 2 and 3 allows the aggregation of multiple VCCs and thus better management of the bandwidth within the backbone network.
VCC Aggregation
While most Virtual Channel Connections (VCCs) within access networks do not require a large amount of bandwidth, the traffic between the different access networks through the backbone network requires the definition of large bandwidth connections. The use of Virtual Path Connections (VPCs) considerably limits the number of VCCs which must be established on the backbone network, while optimizing the bandwidth utilization. The response time is generally reduced, avoiding delays in the different policing processes. While in access networks CBR, VBR or ABR/UBR Virtual Channel Connections (VCCs) are established, the backbone network requires usually ABR or CBR VPCs. These Virtual Path Connections must be able to transport any category of service, without distinction of quality, through the backbone network.
Bandwidth Management
The quality of the process used at the backbone/access networks edges to allocate the bandwidth of a VPC among different individual VCC connections determines the overall performance of the end to end service: short delays for high priority traffic (voice or CBR traffic), and smoothing of low priority traffic (data or ABR traffic) even if, within the backbone network, in the same Virtual Path Connection (VPC), all types of traffic are mixed. The different functions of the process for controlling the traffic are smoothing, queuing, and bandwidth allocation.
Smoothing: a shaping function is used to send the traffic of the Virtual Channel Connections (VCCs) on the Virtual Path Connection (VPC), controlling the maximum transmission rate. Delays between consecutive cells are introduced to space the flow.
Queuing: the shaping function lets the traffic leave the node at a lower rate than available. This induces additional queuing in the node. A good implementation allows the storing of data without loss.
Bandwidth Allocation: within a given Virtual Path Connection (VPC), the bandwidth is allocated among the different VCC connections. Rules must be chosen to fairly allocate the bandwidth of a Virtual Path Connection (VPC) taking into account the category of service of the different VCCs (CBR, VBR, ABR, UBR).
ABR and Bandwidth Adjustable CBR Virtual Path Connections (VPC)
ABR Virtual Path Connections (FIG. 6)
While the Available Bit Rate (ABR) service category is defined in the ATM Forum specifications and provides an efficient bandwidth utilization, its implementation requires important resources in term of:
processing capacity for managing RM-cells along the ABR VPC and continuously (in a time period on the order of a micro or milli second) adjusting the bandwidth, and
additional bandwidth. Per default, one RM-cell is generated every 32 cells, which represents about 3% additional bandwidth only used for the RM-cell traffic.
Solutions based on equivalent principles (dynamic bandwidth adjustment function of the network availability), but characterized by a slower reaction time (minutes or seconds instead of microseconds) are then preferred to ABR service category to save resources.
Bandwidth Adjustable CBR Virtual Path Connection (FIG. 7)
The ATM specifications defined in the ATM Forum do not define a bandwidth adjustable CBR or VPC. This service category is not standard and its implementation depends on the backbone network provider. As illustrated in FIG. 7, when both access network and backbone network are managed by the same network provider, it is possible to define a specific (proprietary) solution for transporting the adjustment information including the VPC transmission rate from the backbone network to the access network. In this case, proprietary RM-cells can be used at the interface between access network and backbone network (between node 2 and node 3). If access and backbone networks are not managed by the same provider, only a standard interface can be used.
FIG. 8 is a view of a network comprising a first access network (access network 1) comprising an end node (node 1) connected to a user 1 and a source node (node 2), a backbone network comprising a plurality of nodes (nodes 3, 4, and 9), and a second access network (access network 2) comprising a destination node (node 5), transit nodes (nodes 6 and 7), and an end node (node 8) connected to a user 2. A CBR VCC is established in the backbone network between nodes 3 and 4, to transmit, to node 4, traffic of end user 1 (VCC1).
The solution according to the present invention is, as shown in FIG. 8, to configure an Available Bit Rate (ABR) Virtual Path Connection (VPC) between nodes 2 and 3 in order to provide this standard interface to the proprietary CBR VPC established in the backbone network. Node 2 will see an ABR VPC, and will react as if an end to end ABR VPC were set-up. In the backbone network, node 3 at the destination of the ABR VPC and at the source of the adjustable CBR VPC, will be in charge of translating the CBR VPC bandwidth adjustments into RM-cells updates on the ABR VPC.
Similarly, an Available Bit Rate (ABR) Virtual Path Connection (VPC) is also configured between nodes 4 and 5 to provide a standard interface to the proprietary CBR VCC established in the backbone network between nodes 3 and 4. In node 5, the traffic is transmitted to end user 2 (VCC2).
The object of the present invention is to provide to an ATM access network a standard and transparent ATM interface for accessing a non standard ATM bandwidth adjustable virtual path connection established on a backbone network between a backbone source node and a backbone destination node, this backbone network and this ATM access network comprising a plurality of nodes interconnected with transmission links. An ATM available bit rate (ABR) virtual path connection is established between the ATM access network and the backbone source node of the bandwidth adjustable virtual path connection. The available bit rate is adjusted according to the adjusted bandwidth of the virtual path connection established on the backbone node.
In a particular embodiment, the bandwidth adjustable virtual path connection is a continuous bit rate (CBR) virtual path connection with dynamic bandwidth adjustment. The backbone network comprises a bandwidth management server connected to each backbone node first, for dynamically computing the bandwidth which is available on backbone transmission links, second, for sharing this bandwidth among the bandwidth adjustable virtual path connections established on the backbone network, third, for balancing among the backbone transmission links, the bandwidth reserved for bandwidth adjustable virtual path connections, and finally for adjusting the bandwidth of these bandwidth adjustable virtual path connections through the respective source nodes.